Actin-Based Cell Protrusion in a 3D Matrix

Environmentally dependent and independent control of 3D cell shape

How cancer cells determine their shape in response to three-dimensional (3D) geometric and mechanical cues is unclear. We develop an approach to quantify the 3D cell shape of over 60,000 melanoma cells in collagen hydrogels using high-throughput stage-scanning oblique plane microscopy (ssOPM). We identify stereotypic and environmentally dependent changes in shape and protrusivity depending on whether a cell is proximal to a flat and rigid surface or is embedded in a soft environment. Environmental sensitivity metrics calculated for small molecules and gene knockdowns identify interactions between the environment and cellular factors that are important for morphogenesis. We show that the Rho guanine nucleotide exchange factor (RhoGEF) TIAM2 contributes to shape determination in environmentally independent ways but that non-muscle myosin II, microtubules, and the RhoGEF FARP1 regulate shape in ways dependent on the microenvironment. Thus, changes in cancer cell shape in response to 3D geometric and mechanical cues are modulated in both an environmentally dependent and independent fashion.

LATS1 controls CTCF chromatin occupancy and hormonal response of 3D-grown breast cancer cells

The cancer epigenome has been studied in cells cultured in two-dimensional (2D) monolayers, but recent studies highlight the impact of the extracellular matrix and the three-dimensional (3D) environment on multiple cellular functions. Here, we report the physical, biochemical, and genomic differences between T47D breast cancer cells cultured in 2D and as 3D spheroids. Cells within 3D spheroids exhibit a rounder nucleus with less accessible, more compacted chromatin, as well as altered expression of ~2000 genes, the majority of which become repressed. Hi-C analysis reveals that cells in 3D are enriched for regions belonging to the B compartment, have decreased chromatin-bound CTCF and increased fusion of topologically associating domains (TADs). Upregulation of the Hippo pathway in 3D spheroids results in the activation of the LATS1 kinase, which promotes phosphorylation and displacement of CTCF from DNA, thereby likely causing the observed TAD fusions. 3D cells show higher chromatin binding of progesterone receptor (PR), leading to an increase in the number of hormone-regulated genes. This effect is in part mediated by LATS1 activation, which favors cytoplasmic retention of YAP and CTCF removal.

Collective cell migration relies on PPP1R15-mediated regulation of the endoplasmic reticulum stress response

Collective cell migration is integral to many developmental and disease processes. Previously, we discovered that protein phosphatase 1 (Pp1) promotes border cell collective migration in the Drosophila ovary. We now report that the Pp1 phosphatase regulatory subunit dPPP1R15 is a critical regulator of border cell migration. dPPP1R15 is an ortholog of mammalian PPP1R15 proteins that attenuate the endoplasmic reticulum (ER) stress response. We show that, in collectively migrating border cells, dPPP1R15 phosphatase restrains an active physiological protein kinase R-like ER kinase- (PERK)-eIF2α-activating transcription factor 4 (ATF4) stress pathway. RNAi knockdown of dPPP1R15 blocks border cell delamination from the epithelium and subsequent migration, increases eIF2α phosphorylation, reduces translation, and drives expression of the stress response transcription factor ATF4. We observe similar defects upon overexpression of ATF4 or the eIF2α kinase PERK. Furthermore, we show that normal border cells express markers of the PERK-dependent ER stress response and require PERK and ATF4 for efficient migration. In many other cell types, unresolved ER stress induces initiation of apoptosis. In contrast, border cells with chronic RNAi knockdown of dPPP1R15 survive. Together, our results demonstrate that the PERK-eIF2α-ATF4 pathway, regulated by dPPP1R15 activity, counteracts the physiological ER stress that occurs during collective border cell migration. We propose that in vivo collective cell migration is intrinsically "stressful," requiring tight homeostatic control of the ER stress response for collective cell cohesion, dynamics, and movement.

Oleate Promotes Triple-Negative Breast Cancer Cell Migration by Enhancing Filopodia Formation through a PLD/Cdc42-Dependent Pathway

Breast cancer, particularly triple-negative breast cancer (TNBC), poses a global health challenge. Emerging evidence has established a positive association between elevated levels of stearoyl-CoA desaturase 1 (SCD1) and its product oleate (OA) with cancer development and metastasis. SCD1/OA leads to alterations in migration speed, direction, and cell morphology in TNBC cells, yet the underlying molecular mechanisms remain elusive. To address this gap, we aim to investigate the impact of OA on remodeling the actin structure in TNBC cell lines, and the underlying signaling. Using TNBC cell lines and bioinformatics tools, we show that OA stimulation induces rapid cell membrane ruffling and enhances filopodia formation. OA treatment triggers the subcellular translocation of Arp2/3 complex and Cdc42. Inhibiting Cdc42, not the Arp2/3 complex, effectively abolishes OA-induced filopodia formation and cell migration. Additionally, our findings suggest that phospholipase D is involved in Cdc42-dependent filopodia formation and cell migration. Lastly, the elevated expression of Cdc42 in breast tumor tissues is associated with a lower survival rate in TNBC patients. Our study outlines a new signaling pathway in the OA-induced migration of TNBC cells, via the promotion of Cdc42-dependent filopodia formation, providing a novel insight for therapeutic strategies in TNBC treatment.

Apical expansion of calvarial osteoblasts and suture patency is dependent on fibronectin cues

The skull roof, or calvaria, is comprised of interlocking plates of bones that encase the brain. Separating these bones are fibrous sutures that permit growth. Currently, we do not understand the instructions for directional growth of the calvaria, a process which is error-prone and can lead to skeletal deficiencies or premature suture fusion (craniosynostosis, CS). Here, we identify graded expression of fibronectin (FN1) in the mouse embryonic cranial mesenchyme (CM) that precedes the apical expansion of calvaria. Conditional deletion of Fn1 or Wasl leads to diminished frontal bone expansion by altering cell shape and focal actin enrichment, respectively, suggesting defective migration of calvarial progenitors. Interestingly, Fn1 mutants have premature fusion of coronal sutures. Consistently, syndromic forms of CS in humans exhibit dysregulated FN1 expression, and we also find FN1 expression altered in a mouse CS model of Apert syndrome. These data support a model of FN1 as a directional substrate for calvarial osteoblast migration that may be a common mechanism underlying many cranial disorders of disparate genetic etiologies.

Dynamically Mapping the Topography and Stiffness of the Leading Edge of Migrating Cells Using AFM in Fast-QI Mode

Cell migration profoundly influences cellular function, often resulting in adverse effects in various pathologies including cancer metastasis. Directly assessing and quantifying the nanoscale dynamics of living cell structure and mechanics has remained a challenge. At the forefront of cell movement, the flat actin modules─the lamellipodium and the lamellum─interact to propel cell migration. The lamellipodium extends from the lamellum and undergoes rapid changes within seconds, making measurement of its stiffness a persistent hurdle. In this study, we introduce the fast-quantitative imaging (fast-QI) mode, demonstrating its capability to simultaneously map both the lamellipodium and the lamellum with enhanced spatiotemporal resolution compared with the classic quantitative imaging (QI) mode. Specifically, our findings reveal nanoscale stiffness gradients in the lamellipodium at the leading edge, where it appears to be slightly thinner and significantly softer than the lamellum. Additionally, we illustrate the fast-QI mode's accuracy in generating maps of height and effective stiffness through a streamlined and efficient processing of force-distance curves. These results underscore the potential of the fast-QI mode for investigating the role of motile cell structures in mechanosensing.

Modeling the extracellular matrix in cell migration and morphogenesis: a guide for the curious biologist

The extracellular matrix (ECM) is a highly complex structure through which biochemical and mechanical signals are transmitted. In processes of cell migration, the ECM also acts as a scaffold, providing structural support to cells as well as points of potential attachment. Although the ECM is a well-studied structure, its role in many biological processes remains difficult to investigate comprehensively due to its complexity and structural variation within an organism. In tandem with experiments, mathematical models are helpful in refining and testing hypotheses, generating predictions, and exploring conditions outside the scope of experiments. Such models can be combined and calibrated with in vivo and in vitro data to identify critical cell-ECM interactions that drive developmental and homeostatic processes, or the progression of diseases. In this review, we focus on mathematical and computational models of the ECM in processes such as cell migration including cancer metastasis, and in tissue structure and morphogenesis. By highlighting the predictive power of these models, we aim to help bridge the gap between experimental and computational approaches to studying the ECM and to provide guidance on selecting an appropriate model framework to complement corresponding experimental studies.

Imaging actin organisation and dynamics in 3D

The actin cytoskeleton plays a critical role in cell architecture and the control of fundamental processes including cell division, migration and survival. The dynamics and organisation of F-actin have been widely studied in a breadth of cell types on classical two-dimensional (2D) surfaces. Recent advances in optical microscopy have enabled interrogation of these cytoskeletal networks in cells within three-dimensional (3D) scaffolds, tissues and in vivo. Emerging studies indicate that the dimensionality experienced by cells has a profound impact on the structure and function of the cytoskeleton, with cells in 3D environments exhibiting cytoskeletal arrangements that differ to cells in 2D environments. However, the addition of a third (and fourth, with time) dimension leads to challenges in sample preparation, imaging and analysis, necessitating additional considerations to achieve the required signal-to-noise ratio and spatial and temporal resolution. Here, we summarise the current tools for imaging actin in a 3D context and highlight examples of the importance of this in understanding cytoskeletal biology and the challenges and opportunities in this domain.

3D matrix adhesion feedback controls nuclear force coupling to drive invasive cell migration

Cell invasion is a multi-step process, initiated by the acquisition of a migratory phenotype and the ability to move through complex 3D extracellular environments. We determine the composition of cell-matrix adhesion complexes of invasive breast cancer cells in 3D matrices and identify an interaction complex required for invasive migration. βPix and myosin18A (Myo18A) drive polarized recruitment of non-muscle myosin 2A (NM2A) to adhesion complexes at the tips of protrusions. Actomyosin force engagement then displaces the Git1-βPix complex from paxillin, establishing a feedback loop for adhesion maturation. We observe active force transmission to the nucleus during invasive migration that is needed to pull the nucleus forward. The recruitment of NM2A to adhesions creates a non-muscle myosin isoform gradient, which extends from the protrusion to the nucleus. We postulate that this gradient facilitates coupling of cell-matrix interactions at the protrusive cell front with nuclear movement, enabling effective invasive migration and front-rear cell polarity.

Extracellular matrix stiffness activates mechanosensitive signals but limits breast cancer cell spheroid proliferation and invasion

Breast cancer is characterized by physical changes that occur in the tumor microenvironment throughout growth and metastasis of tumors. Extracellular matrix stiffness increases as tumors develop and spread, with stiffer environments thought to correlate with poorer disease prognosis. Changes in extracellular stiffness and other physical characteristics are sensed by integrins which integrate these extracellular cues to intracellular signaling, resulting in modulation of proliferation and invasion. However, the co-ordination of mechano-sensitive signaling with functional changes to groups of tumor cells within 3-dimensional environments remains poorly understood. Here we provide evidence that increasing the stiffness of collagen scaffolds results in increased activation of ERK1/2 and YAP in human breast cancer cell spheroids. We also show that ERK1/2 acts upstream of YAP activation in this context. We further demonstrate that YAP, matrix metalloproteinases and actomyosin contractility are required for collagen remodeling, proliferation and invasion in lower stiffness scaffolds. However, the increased activation of these proteins in higher stiffness 3-dimensional collagen gels is correlated with reduced proliferation and reduced invasion of cancer cell spheroids. Our data collectively provide evidence that higher stiffness 3-dimensional environments induce mechano-signaling but contrary to evidence from 2-dimensional studies, this is not sufficient to promote pro-tumorigenic effects in breast cancer cell spheroids.

Extracellular vesicles on the move: Traversing the complex matrix of tissues

Extracellular vesicles are small particles involved in intercellular signaling. They are produced by virtually all cell types, transport biological molecules, and are released into the extracellular space. Studies on extracellular vesicles have become more numerous in recent years, leading to promising research on their potential impact on health and disease. Despite significant progress in understanding the bioactivity of extracellular vesicles, most in vitro and in vivo studies overlook their transport through the extracellular matrix in tissues. The interaction or free diffusion of extracellular vesicles in their environment can provide valuable insights into their efficacy and function. Therefore, understanding the factors that influence the transport of extracellular vesicles in the extracellular matrix is essential for the development of new therapeutic approaches that involve the use of these extracellular vesicles. This review discusses the importance of the interaction between extracellular vesicles and the extracellular matrix and the different factors that influence their diffusion. In addition, we evaluate their role in tissue homeostasis, pathophysiology, and potential clinical applications. Understanding the complex interaction between extracellular vesicles and the extracellular matrix is critical in order to develop effective strategies to target specific cells and tissues in a wide range of clinical applications.

Fiber Microarchitecture in Interpenetrating Collagen-Alginate Hydrogel with Tunable Mechanical Plasticity Regulates Tumor Cell Migration

The fiber structures of tumor microenvironment (TME) are well-known in regulating tumor cell behaviors, and the plastic remolding of TME has recently been suggested to enhance tumor metastasis as well. However, the interrelationship between the fiber microarchitecture and matrix plasticity is inextricable by existing in vitro models. The individual roles of fiber microarchitecture and matrix plasticity in tuning tumor cell behaviors remain elusive. This study develops an interpenetrating collagen-alginate hydrogel platform with independently tunable matrix plasticity and fiber microarchitecture through an interpenetrating strategy of alginate networks and collagen I networks. With this hydrogel platform, it is demonstrated that tumor cells in high plasticity hydrogels are more extensive and aggressive than in low plasticity hydrogels and fiber structures only have influence in high plasticity hydrogels. The study further elucidates the underlying mechanisms through analyzing the distribution of forces within the matrix and tracking the focal adhesions (FAs) and finds that highly plastic hydrogels can activate the FAs formation, whereas the maturation and stability of FAs are dominated by fiber dispersion. This study not only establishes new ideas on how cells interact with TME cues but also would help to further finely tailor engineered hydrogel platforms for studying tumor behaviors in vitro.

Compression drives diverse transcriptomic and phenotypic adaptations in melanoma

Physical forces are prominent during tumor progression. However, it is still unclear how they impact and drive the diverse phenotypes found in cancer. Here, we apply an integrative approach to investigate the impact of compression on melanoma cells. We apply bioinformatics to screen for the most significant compression-induced transcriptomic changes and investigate phenotypic responses. We show that compression-induced transcriptomic changes are associated with both improvement and worsening of patient prognoses. Phenotypically, volumetric compression inhibits cell proliferation and cell migration. It also induces organelle stress and intracellular oxidative stress and increases pigmentation in malignant melanoma cells and normal human melanocytes. Finally, cells that have undergone compression become more resistant to cisplatin treatment. Our findings indicate that volumetric compression is a double-edged sword for melanoma progression and drives tumor evolution.

Experimental and theoretical model for the origin of coiling of cellular protrusions around fibers

Protrusions at the leading-edge of a cell play an important role in sensing the extracellular cues during cellular spreading and motility. Recent studies provided indications that these protrusions wrap (coil) around the extracellular fibers. However, the physics of this coiling process, and the mechanisms that drive it, are not well understood. We present a combined theoretical and experimental study of the coiling of cellular protrusions on fibers of different geometry. Our theoretical model describes membrane protrusions that are produced by curved membrane proteins that recruit the protrusive forces of actin polymerization, and identifies the role of bending and adhesion energies in orienting the leading-edges of the protrusions along the azimuthal (coiling) direction. Our model predicts that the cell's leading-edge coils on fibers with circular cross-section (above some critical radius), but the coiling ceases for flattened fibers of highly elliptical cross-section. These predictions are verified by 3D visualization and quantitation of coiling on suspended fibers using Dual-View light-sheet microscopy (diSPIM). Overall, we provide a theoretical framework, supported by experiments, which explains the physical origin of the coiling phenomenon.

Unveiling the physics underlying symmetry breaking of the actin cytoskeleton: An artificial cell-based approach

Single-cell behaviors cover many biological functions, such as cell division during morphogenesis and tissue metastasis, and cell migration during cancer cell invasion and immune cell responses. Symmetry breaking of the positioning of organelles and the cell shape are often associated with these biological functions. One of the main players in symmetry breaking at the cellular scale is the actin cytoskeleton, comprising actin filaments and myosin motors that generate contractile forces. However, because the self-organization of the actomyosin network is regulated by the biochemical signaling in cells, how the mechanical contraction of the actin cytoskeleton induces diverse self-organized behaviors and drives the cell-scale symmetry breaking remains unclear. In recent times, to understand the physical underpinnings of the symmetry breaking exhibited in the actin cytoskeleton, artificial cell models encapsulating the cytoplasmic actomyosin networks covered with lipid monolayers have been developed. By decoupling the actomyosin mechanics from the complex biochemical signaling within living cells, this system allows one to study the self-organization of actomyosin networks confined in cell-sized spaces. We review the recent developments in the physics of confined actomyosin networks and provide future perspectives on the artificial cell-based approach. This review article is an extended version of the Japanese article, The Physical Principle of Cell Migration Under Confinement: Artificial Cell-based Bottom-up Approach, published in SEIBUTSU BUTSURI Vol. 63, p. 163-164 (2023).

A minimal cell model for lamellipodia-based cellular dynamics and migration

One ubiquitous cellular structure for performing various tasks, such as spreading and migration over external surfaces, is the sheet-like protrusion called a lamellipodium, which propels the leading edge of the cell. Despite the detailed knowledge about the many components of this cellular structure, it is not yet fully understood how these components self-organize spatiotemporally to form lamellipodia. We review here recent theoretical works where we have demonstrated that membrane-bound protein complexes that have intrinsic curvature and recruit the protrusive forces of the cytoskeleton result in a simple, yet highly robust, organizing feedback mechanism that organizes the cytoskeleton and the membrane. This self-organization mechanism accounts for the formation of flat lamellipodia at the leading edge of cells spreading over adhesive substrates, allowing for the emergence of a polarized, motile 'minimal cell' model. The same mechanism describes how lamellipodia organize to drive robust engulfment of particles during phagocytosis and explains in simple physical terms the spreading and migration of cells over fibers and other curved surfaces. This Review highlights that despite the complexity of cellular composition, there might be simple general physical principles that are utilized by the cell to drive cellular shape dynamics.

Plasticity of cancer invasion and energy metabolism

Energy deprivation is a frequent adverse event in tumors that is caused by mutations, malperfusion, hypoxia, and nutrition deficit. The resulting bioenergetic stress leads to signaling and metabolic adaptation responses in tumor cells, secures survival, and adjusts migration activity. The kinetic responses of cancer cells to energy deficit were recently identified, including a switch of invasive cancer cells to energy-conservative amoeboid migration and an enhanced capability for distant metastasis. We review the energy programs employed by different cancer invasion modes including collective, mesenchymal, and amoeboid migration, as well as their interconversion in response to energy deprivation, and we discuss the consequences for metastatic escape. Understanding the energy requirements of amoeboid and other dissemination strategies offers rationales for improving therapeutic targeting of metastatic cancer progression.

Extracellular alkaline pH enhances migratory behaviors of hepatocellular carcinoma cells as a caution against the indiscriminate application of alkalinizing drug therapy: In vitro microscopic studies

The migratory process is a highly organized, differentiated, and polarized stage by which many signaling pathways are regulated to control cell migration. Since the significant evidence of migrating cells is the reorganization of the cytoskeleton. In the recent study, the cell migration model was assessed on the fact that any disruption obtained in the cellular monolayer confluent, may cause stimulation for surrounding cells to migrate. We attempt to demonstrate the morphological alterations associated with these migrating cells. In this case, sterilized 1 N NaOH (1 µl) was used as alkaline burnt. It leads to scratching the monolayer of hepatocellular carcinoma (HLF cell line) allowing cells to lose their connection. Scanning electron microscopy (SEM), fluorescence microscopy, light inverted microscopy, and dark field were used for discovering the morphological alterations associated with migrating cancer cells. The findings show that cells exhibited distinctive alterations including a polarizing stage, accumulation of the actin nodules in front of the nucleus, and protrusions. Nuclei appeared as lobulated shapes during migration. Lamellipodia and uropod were extended as well. Additionally, TGFβ1 proved its expression in HLF and SNU449 after their stimulation. It is demonstrated that hepatocellular carcinoma cells can migrate after their stimulation and there is a caution against the indiscriminate application of alkalinizing drug therapy.

High-Throughput Electromechanical Coupling Chip Systems for Real-Time 3D Invasion/Migration Assay of Cells

Cell invasion/migration through three-dimensional (3D) tissues is not only essential for physiological/pathological processes, but a hallmark of cancer malignancy. However, how to quantify spatiotemporal dynamics of 3D cell migration/invasion is challenging. Here, this work reports a 3D cell invasion/migration assay (3D-CIMA) based on electromechanical coupling chip systems, which can monitor spatiotemporal dynamics of 3D cell invasion/migration in a real-time, label-free, nondestructive, and high-throughput way. In combination with 3D topological networks and complex impedance detection technology, this work shows that 3D-CIMA can quantitively characterize collective invasion/migration dynamics of cancer cells in 3D extracellular matrix (ECM) with controllable biophysical/biomechanical properties. More importantly, this work further reveals that it has the capability to not only carry out quantitative evaluation of anti-tumor drugs in 3D microenvironments that minimize the impact of cell culture dimensions, but also grade clinical cancer specimens. The proposed 3D-CIMA offers a new quantitative methodology for investigating cell interactions with 3D extracellular microenvironments, which has potential applications in various fields like mechanobiology, drug screening, and even precision medicine.

ARF3 weights the balance for prostate cancer metastasis

Patrick T. Caswell discusses work from Bryant and colleagues (2023. J. Cell Biol.https://doi.org/10.1083/jcb.202206115) which shows how ARF3 impacts metastasis in prostate cancer by regulating a switch between modes of collective invasion.

Light-sheet microscopy reveals dorsoventral asymmetric membrane dynamics of Amoeba proteus during pressure-driven locomotion

Amoebae are found all around the world and play an essential role in the carbon cycle in the environment. Therefore, the behavior of amoebae is a crucial factor when considering the global environment. Amoebae change their distribution through amoeboid locomotion, which are classified into several modes. In the pressure-driven mode, intracellular hydrostatic pressure generated by the contraction of cellular cortex actomyosin causes the pseudopod to extend. During amoeboid locomotion, the cellular surface exhibits dynamic deformation. Therefore, to understand the mechanism of amoeboid locomotion, it is important to characterize cellular membrane dynamics. Here, to clarify membrane dynamics during pressure-driven amoeboid locomotion, we developed a polkadot membrane staining method and performed light-sheet microscopy in Amoeba proteus, which exhibits typical pressure-driven amoeboid locomotion. It was observed that the whole cell membrane moved in the direction of movement, and the dorsal cell membrane in the posterior part of the cell moved more slowly than the other membrane. In addition, membrane complexity varied depending on the focused characteristic size of the membrane structure, and in general, the dorsal side was more complex than the ventral side. In summary, the membrane dynamics of Amoeba proteus during pressure-driven locomotion are asymmetric between the dorsal and ventral sides. This article has an associated interview with the co-first authors of the paper.

Apical expansion of calvarial osteoblasts and suture patency is dependent on graded fibronectin cues

The skull roof, or calvaria, is comprised of interlocking plates of bone. Premature suture fusion (craniosynostosis, CS) or persistent fontanelles are common defects in calvarial development. Although some of the genetic causes of these disorders are known, we lack an understanding of the instructions directing the growth and migration of progenitors of these bones, which may affect the suture patency. Here, we identify graded expression of Fibronectin (FN1) protein in the mouse embryonic cranial mesenchyme (CM) that precedes the apical expansion of calvarial osteoblasts. Syndromic forms of CS exhibit dysregulated FN1 expression, and we find FN1 expression is altered in a mouse CS model as well. Conditional deletion of Fn1 in CM causes diminished frontal bone expansion by altering cell polarity and shape. To address how osteoprogenitors interact with the observed FN1 prepattern, we conditionally ablate Wasl/N-Wasp to disrupt F-actin junctions in migrating cells, impacting lamellipodia and cell-matrix interaction. Neural crest-targeted deletion of Wasl results in a diminished actin network and reduced expansion of frontal bone primordia similar to conditional Fn1 mutants. Interestingly, defective calvaria formation in both the Fn1 and Wasl mutants occurs without a significant change in proliferation, survival, or osteogenesis. Finally, we find that CM-restricted Fn1 deletion leads to premature fusion of coronal sutures. These data support a model of FN1 as a directional substrate for calvarial osteoblast migration that may be a common mechanism underlying many cranial disorders of disparate genetic etiologies.

Customizable 3D printed perfusion bioreactor for the engineering of stem cell microenvironments

Faithful modeling of tissues and organs requires the development of systems reflecting their dynamic 3D cellular architecture and organization. Current technologies suffer from a lack of design flexibility and complex prototyping, preventing their broad adoption by the scientific community. To make 3D cell culture more available and adaptable we here describe the use of the fused deposition modeling (FDM) technology to rapid-prototype 3D printed perfusion bioreactors. Our 3D printed bioreactors are made of polylactic acid resulting in reusable systems customizable in size and shape. Following design confirmation, our bioreactors were biologically validated for the culture of human mesenchymal stromal cells under perfusion for up to 2 weeks on collagen scaffolds. Microenvironments of various size/volume (6-12 mm in diameter) could be engineered, by modulating the 3D printed bioreactor design. Metabolic assay and confocal microscopy confirmed the homogenous mesenchymal cell distribution throughout the material pores. The resulting human microenvironments were further exploited for the maintenance of human hematopoietic stem cells. Following 1 week of stromal coculture, we report the recapitulation of 3D interactions between the mesenchymal and hematopoietic fractions, associated with a phenotypic expansion of the blood stem cell populations.Our data confirm that perfusion bioreactors fit for cell culture can be generated using a 3D printing technology and exploited for the 3D modeling of complex stem cell systems. Our approach opens the gates for a more faithful investigation of cellular processes in relation to a dynamic 3D microenvironment.

Stiff matrix induced srGAP2 tension gradients control migration direction in triple-negative breast cancer

Rationale: Cells migrating through interstitial matrix enables stiffening of the tumor micro-environment. To overcome the stiff resistance of extracellular matrix, aggressive cells require the extracellular mechanosensory activation and intracellular tension response. Mechanotransduction linker srGAP2 can synergistically control the mechanical-biochemical process of malignant cell migration. Methods: To mimic the tumor micro-environment containing abundant collagen fibers and moving durotaxis of triple-negative breast cancer cells, the stiff-directed matrix was established. The newly designed srGAP2 tension probe was used to real-time supervise srGAP2 tension in living cells. The phosphorylation sites responsible for srGAP2 tension were identified by phosphorylated mutagenesis. Transwell assays and Xenograft mouse model were performed to evaluate TNBC cells invasiveness in vitro and in vivo. Fluorescence staining and membrane protein isolation were used to detect protein localization. Results: The present study shows srGAP2 serves as a linker to transmit the mechanical signals among cytoskeleton and membrane. SrGAP2 exhibits tension gradients among different parts in the stiff-directionally migrating triple-negative breast cancer cells. Cells showing the polarized tension that increased in the leading edge move faster, particularly guided by the stiff interstitial matrix. The srGAP2 tension-directed cell migration results from the upstream events of PKCα-mediated phosphorylation at Ser²⁰⁶ in the F-bar domain of srGAP2. In addition, Syndecan-4 (SDC4), a transmembrane mechanoreceptor protein, drives PKCα regional recruit on the area of membrane trending deformation, which requires the distinct extent of extracellular mechanics. Conclusion: SDC4-PKCα polarized distribution leads to the intracellular tension gradient of srGAP2, presenting the extra- and intracellular physiochemical integration and essential for persistent cell migration in stiff matrix and caner progression. Targeting the srGAP2-related physicochemical signaling could be developed into the therapeutic strategies of inhibiting breast cancer cell invasion and durotaxis.

Unravelling cell migration: defining movement from the cell surface

Cell motility is essential for life and development. Unfortunately, cell migration is also linked to several pathological processes, such as cancer metastasis. Cells' ability to migrate relies on many actors. Cells change their migratory strategy based on their phenotype and the properties of the surrounding microenvironment. Cell migration is, therefore, an extremely complex phenomenon. Researchers have investigated cell motility for more than a century. Recent discoveries have uncovered some of the mysteries associated with the mechanisms involved in cell migration, such as intracellular signaling and cell mechanics. These findings involve different players, including transmembrane receptors, adhesive complexes, cytoskeletal components , the nucleus, and the extracellular matrix. This review aims to give a global overview of our current understanding of cell migration.

Non-muscle myosin II and the plasticity of 3D cell migration

Confined cells migrating through 3D environments are also constrained by the laws of physics, meaning for every action there must be an equal and opposite reaction for cells to achieve motion. Fascinatingly, there are several distinct molecular mechanisms that cells can use to move, and this is reflected in the diverse ways non-muscle myosin II (NMII) can generate the mechanical forces necessary to sustain 3D cell migration. This review summarizes the unique modes of 3D migration, as well as how NMII activity is regulated and localized within each of these different modes. In addition, we highlight tropomyosins and septins as two protein families that likely have more secrets to reveal about how NMII activity is governed during 3D cell migration. Together, this information suggests that investigating the mechanisms controlling NMII activity will be helpful in understanding how a single cell transitions between distinct modes of 3D migration in response to the physical environment.

Vimentin and cytokeratin: Good alone, bad together

The cytoskeleton plays an integral role in maintaining the integrity of epithelial cells. Epithelial cells primarily employ cytokeratin in their cytoskeleton, whereas mesenchymal cells use vimentin. During the epithelial-mesenchymal transition (EMT), cytokeratin-positive epithelial cells begin to express vimentin. EMT induces stem cell properties and drives metastasis, chemoresistance, and tumor relapse. Most studies of the functions of cytokeratin and vimentin have relied on the use of either epithelial or mesenchymal cell types. However, it is important to understand how these two cytoskeleton intermediate filaments function when co-expressed in cells undergoing EMT. Here, we discuss the individual and shared functions of cytokeratin and vimentin that coalesce during EMT and how alterations in intermediate filament expression influence carcinoma progression.

A meta-analysis indicates that the regulation of cell motility is a non-intrinsic function of chemoattractant receptors that is governed independently of directional sensing

Chemoattraction, defined as the migration of a cell toward a source of a chemical gradient, is controlled by chemoattractant receptors. Chemoattraction involves two basic activities, namely, directional sensing, a molecular mechanism that detects the direction of a source of chemoattractant, and actin-based motility, which allows the migration of a cell towards it. Current models assume first, that chemoattractant receptors govern both directional sensing and motility (most commonly inducing an increase in the migratory speed of the cells, i.e. chemokinesis), and, second, that the signaling pathways controlling both activities are intertwined. We performed a meta-analysis to reassess these two points. From this study emerge two main findings. First, although many chemoattractant receptors govern directional sensing, there are also receptors that do not regulate cell motility, suggesting that is the ability to control directional sensing, not motility, that best defines a chemoattractant receptor. Second, multiple experimental data suggest that receptor-controlled directional sensing and motility can be controlled independently. We hypothesize that this independence may be based on the existence of separated signalling modules that selectively govern directional sensing and motility in chemotactic cells. Together, the information gathered can be useful to update current models representing the signalling from chemoattractant receptors. The new models may facilitate the development of strategies for a more effective pharmacological modulation of chemoattractant receptor-controlled chemoattraction in health and disease.

Loss of the fructose transporter SLC2A5 inhibits cancer cell migration

Metastasis is the primary cause of cancer patient death and the elevation of SLC2A5 gene expression is often observed in metastatic cancer cells. Here we evaluated the importance of SLC2A5 in cancer cell motility by silencing its gene. We discovered that CRISPR/Cas9-mediated inactivation of the SLC2A5 gene inhibited cancer cell proliferation and migration in vitro as well as metastases in vivo in several animal models. Moreover, SLC2A5-attenuated cancer cells exhibited dramatic alterations in mitochondrial architecture and localization, uncovering the importance of SLC2A5 in directing mitochondrial function for cancer cell motility and migration. The direct association of increased abundance of SLC2A5 in cancer cells with metastatic risk in several types of cancers identifies SLC2A5 as an important therapeutic target to reduce or prevent cancer metastasis.

Time-Series Clustering of Single-Cell Trajectories in Collective Cell Migration

Simple Summary

In this study, we normalized trajectories containing both mesenchymal and epithelial cells to remove the effect of cell location on clustering, and performed a dimensionality reduction on the time series data before clustering. When the clustering results were superimposed on the trajectories prior to normalization, the results still showed similarities in location, indicating that this method can find cells with similar migration patterns. These data highlight the reliability of this method in identifying consistent migration patterns in collective cell migration.

Abstract

Collective invasion drives multicellular cancer cells to spread to surrounding normal tissues. To fully comprehend metastasis, the methodology of analysis of individual cell migration in tissue should be well developed. Extracting and classifying cells with similar migratory characteristics in a colony would facilitate an understanding of complex cell migration patterns. Here, we used electrospun fibers as the extracellular matrix for the in vitro modeling of collective cell migration, clustering of mesenchymal and epithelial cells based on trajectories, and analysis of collective migration patterns based on trajectory similarity. We normalized the trajectories to eliminate the effect of cell location on clustering and used uniform manifold approximation and projection to perform dimensionality reduction on the time-series data before clustering. When the clustering results were superimposed on the trajectories before normalization, the results still exhibited positional similarity, thereby demonstrating that this method can identify cells with similar migration patterns. The same cluster contained both mesenchymal and epithelial cells, and this result was related to cell location and cell division. These data highlight the reliability of this method in identifying consistent migration patterns during collective cell migration. This provides new insights into the epithelial–mesenchymal interactions that affect migration patterns.

T Cells Chemotaxis Migration Studies with a Multi-Channel Microfluidic Device

Immune surveillance is dependent on lymphocyte migration and targeted recruitment. This can involve different modes of cell motility ranging from random walk to highly directional environment-guided migration driven by chemotaxis. This study protocol describes a flow-based microfluidic device to perform quantitative multiplex cell migration assays with the potential to investigate in real time the migratory response of T cells at the population or single-cell level. The device also allows for subsequent in situ fixation and direct fluorescence analysis of the cells in the microchannel.

The role of miR-200 family in the regulation of hallmarks of cancer

MiRNAs are short non-coding RNAs that regulate gene expression post-transcriptionally contributing to the development of different diseases including cancer. The miR-200 family consists of five members, miR-200a, miR-200b, miR-200c, miR-141, and miR-429. Their expression is dysregulated in cancer tissue and their level is altered in the body fluids of cancer patients. Moreover, the levels of miR-200 family members correlate with clinical parameters such as cancer patients' survival which makes them potentially useful as diagnostic and prognostic biomarkers. MiRNAs can act as either oncomiRs or tumor suppressor miRNAs depending on the target genes and their role in the regulation of key oncogenic signaling pathways. In most types of cancer, the miR-200 family acts as tumor suppressor miRNA and regulates all features of cancer. In this review, we summarized the expression pattern of the miR-200 family in different types of cancer and their potential utility as biomarkers. Moreover, we comprehensively described the role of miR-200 family members in the regulation of all hallmarks of cancer proposed by Hanahan and Weinberg with the focus on the epithelial-mesenchymal transition, invasiveness, and metastasis of tumor cells.

ARHGEF9 regulates melanoma morphogenesis in environments with diverse geometry and elasticity by promoting filopodial-driven adhesion

Rho GTP Exchange Factors (RhoGEFs) and Rho GTPase Activating Proteins (RhoGAPs) are large families of molecules that regulate shape determination in all eukaryotes. In pathologies such as melanoma, RhoGEF and RhoGAP activity underpins the ability of cells to invade tissues of varying elasticity. To identify RhoGEFs and RhoGAPs that regulate melanoma cell shape on soft and/or stiff materials, we performed genetic screens, in tandem with single-cell quantitative morphological analysis. We show that ARHGEF9/Collybistin (Cb) is essential for cell shape determination on both soft and stiff materials, and in cells embedded in 3D soft hydrogel. ARHGEF9 is required for melanoma cells to invade 3D matrices. Depletion of ARHGEF9 results in loss of tension at focal adhesions decreased cell-wide contractility, and the inability to stabilize protrusions. Taken together we show that ARHGEF9 promotes the formation of actin-rich filopodia, which serves to establish and stabilize adhesions and determine melanoma cell shape.

Myocyte Culture with Decellularized Skeletal Muscle Sheet with Observable Interaction with the Extracellular Matrix

In skeletal muscles, muscle fibers are highly organized and bundled within the basement membrane. Several microfabricated substrate models have failed to mimic the macrostructure of native muscle, including various extracellular matrix (ECM) proteins. Therefore, we developed and evaluated a system using decellularized muscle tissue and mouse myoblasts C2C12 to analyze the interaction between native ECM and myocytes. Chicken skeletal muscle was sliced into sheets and decellularized to prepare decellularized skeletal muscle sheets (DSMS). C2C12 was then seeded and differentiated on DSMS. Immunostaining for ECM molecules was performed to examine the relationship between myoblast adhesion status, myotube orientation, and collagen IV orientation. Myotube survival in long-term culture was confirmed by calcein staining. C2C12 myoblasts adhered to scaffolds in DSMS and developed adhesion plaques and filopodia. Furthermore, C2C12 myotubes showed orientation along the ECM orientation within DSMS. Compared to plastic dishes, detachment was less likely to occur on DSMS, and long-term incubation was possible. This culture technique reproduces a cell culture environment reflecting the properties of living skeletal muscle, thereby allowing studies on the interaction between the ECM and myocytes.

Follow that cell: leukocyte migration in L-plastin mutant zebrafish

Actin assemblies are important in motile cells such as leukocytes which form dynamic plasma membrane extensions or podia. L-plastin (LCP1) is a leukocyte-specific calcium-dependent actin-bundling protein that, in mammals, is known to affect immune cell migration. Previously, we generated CRISPR/Cas9 engineered zebrafish lacking L-plastin (lcp1-/-) and reported that they had reduced survival to adulthood, suggesting that lack of this actin-bundler might negatively affect the immune system. To test this hypothesis, we examined the distribution and migration of neutrophils and macrophages in the transparent tail of early zebrafish larvae using cell-specific markers and an established wound-migration assay. Knockout larvae were similar to their heterozygous siblings in having equal body sizes and comparable numbers of neutrophils in caudal hematopoietic tissue at two days post-fertilization, indicating no gross defect in neutrophil production or developmental migration. When stimulated by a tail wound, all genotypes of neutrophils were equally migratory in a two-hour window. However for macrophages we observed both migration defects and morphological differences. L-plastin knockout macrophages (lcp1 -/-) still homed to wounds but were slower, less directional and had a star-like morphology with many leading and trailing projections. In contrast, heterozygous macrophages lcp1 (+/-) were faster, more directional, and had a streamlined, slug-like morphology. Overall, these findings show that in larval zebrafish L-plastin knockout primarily affects the macrophage response with possible consequences for organismal immunity. Consistent with our observations, we propose a model in which cytoplasmic L-plastin negatively regulates macrophage integrin adhesion by holding these transmembrane heterodimers in a 'clasped', inactive form and is a necessary part of establishing macrophage polarity during chemokine-induced motility. This article is protected by copyright. All rights reserved.

A mechanistic protrusive-based model for 3D cell migration

Cell migration is essential for a variety of biological processes, such as embryogenesis, wound healing, and the immune response. After more than a century of research-mainly on flat surfaces-, there are still many unknowns about cell motility. In particular, regarding how cells migrate within 3D matrices, which more accurately replicate in vivo conditions. We present a novel in silico model of 3D mesenchymal cell migration regulated by the chemical and mechanical profile of the surrounding environment. This in silico model considers cell's adhesive and nuclear phenotypes, the effects of the steric hindrance of the matrix, and cells ability to degradate the ECM. These factors are crucial when investigating the increasing difficulty that migrating cells find to squeeze their nuclei through dense matrices, which may act as physical barriers. Our results agree with previous in vitro observations where fibroblasts cultured in collagen-based hydrogels did not durotax toward regions with higher collagen concentrations. Instead, they exhibited an adurotactic behavior, following a more random trajectory. Overall, cell's migratory response in 3D domains depends on its phenotype, and the properties of the surrounding environment, that is, 3D cell motion is strongly dependent on the context.

Cofilactin filaments regulate filopodial structure and dynamics in neuronal growth cones

Cofilin is best known for its ability to sever actin filaments and facilitate cytoskeletal recycling inside of cells, but at higher concentrations in vitro, cofilin stabilizes a more flexible, hyper-twisted state of actin known as “cofilactin”. While this filament state is well studied, a structural role for cofilactin in dynamic cellular processes has not been observed. With a combination of cryo-electron tomography and fluorescence imaging in neuronal growth cones, we observe that filopodial actin filaments switch between a fascin-linked and a cofilin-decorated state, and that cofilactin is associated with a variety of dynamic events within filopodia. The switch to cofilactin filaments occurs in a graded fashion and correlates with a decline in fascin cross-linking within the filopodia, which is associated with curvature in the bundle. Our tomographic data reveal that the hyper-twisting of actin from cofilin binding leads to a rearrangement of filament packing, which largely excludes fascin from the base of filopodia. Our results provide mechanistic insight into the fundamentals of cytoskeletal remodeling inside of confined cellular spaces, and how the interplay between fascin and cofilin regulates the dynamics of searching filopodia.

In this manuscript the authors show that Filopodia switch between bundles of fascin-crosslinked actin and cofilin-decorated filaments, which exclude fascin binding due to altered structure and packing, as well as affect filopodial searching dynamics.

Directed invasion of cancer cell spheroids inside 3D collagen matrices oriented by microfluidic flow in experiment and simulation

Invasion is strongly influenced by the mechanical properties of the extracellular matrix. Here, we use microfluidics to align fibers of a collagen matrix and study the influence of fiber orientation on invasion from a cancer cell spheroid. The microfluidic setup allows for highly oriented collagen fibers of tangential and radial orientation with respect to the spheroid, which can be described by finite element simulations. In invasion experiments, we observe a strong bias of invasion towards radial as compared to tangential fiber orientation. Simulations of the invasive behavior with a Brownian diffusion model suggest complete blockage of migration perpendicularly to fibers allowing for migration exclusively along fibers. This slows invasion toward areas with tangentially oriented fibers down, but does not prevent it.

Cytoskeletal dynamics regulates stromal invasion behavior of distinct liver cancer subtypes

Drug treatment against liver cancer has limited efficacy due to heterogeneous response among liver cancer subtypes. In addition, the functional biophysical phenotypes which arise from this heterogeneity and contribute to aggressive invasive behavior remain poorly understood. This study interrogated how heterogeneity in liver cancer subtypes contributes to differences in invasive phenotypes and drug response. Utilizing histological analysis, quantitative 2D invasion metrics, reconstituted 3D hydrogels, and bioinformatics, our study linked cytoskeletal dynamics to differential invasion profiles and drug resistance in liver cancer subtypes. We investigated cytoskeletal regulation in 2D and 3D culture environments using two liver cancer cell lines, SNU-475 and HepG2, chosen for their distinct cytoskeletal features and invasion profiles. For SNU-475 cells, a model for aggressive liver cancer, many cytoskeletal inhibitors abrogated 2D migration but only some suppressed 3D migration. For HepG2 cells, cytoskeletal inhibition did not significantly affect 3D migration but did affect proliferative capabilities and spheroid core growth. This study highlights cytoskeleton driven phenotypic variation, their consequences and coexistence within the same tumor, as well as efficacy of targeting biophysical phenotypes that may be masked in traditional screens against tumor growth.

Treatment for liver cancer is complicated by its various subtypes, which show different responses to anticancer drugs. This study demonstrates the effectiveness of targeting biophysical phenotypes related to cytoskeleton properties that are usually masked in traditional drug screens.

PRR11 induces filopodia formation and promotes cell motility via recruiting ARP2/3 complex in non-small cell lung cancer cells

Filopodia, a finger-like structure and actin-rich plasma-membrane protrusion at the leading edge of the cell, has important roles in cell motility. However, the mechanisms of filopodia generation are not well-understood via the actin-related protein 2/3 (ARP2/3) complex in Non-Small Cell Lung Cancer (NSCLC) cells. We previously have demonstrated that PRR11 associates with the ARP2/3 complex to regulate cytoskeleton-nucleoskeleton assembly and chromatin remodeling. In this study, we further demonstrate that PRR11 involves in filopodia formation, focal adhesion turnover and cell motility through ARP2/3 complex. Cell phenotype assays revealed that the silencing of PRR11 increased cellular size and inhibited cell motility in NSCLC cells. Mechanistically, PRR11 recruited and co-localized with Arp2 at the membrane protrusion to promote filopodia formation but not lamellipodia formation. Notably, PRR11 mutant deletion of the proline-rich region 2 (amino acid residues 185–200) abrogated the effect of filopodia formation. In addition, PRR11-depletion inhibited filopodial actin filaments assembly and increased the level of active integrin β1 in the cell surface, whereas reduced the phosphorylation level of focal adhesion kinase (FAK^Y397) to repress focal adhesion turnover and cell motility in NSCLC cells. Taken together, our findings indicate that PRR11 has critical roles in controlling filopodia formation, focal adhesion turnover and cell motility by recruiting ARP2/3 complex, thus dysregualted expression of PRR11 potentially facilitates tumor metastasis in NSCLC cells.

Dynamics of the Actin Cytoskeleton at Adhesion Complexes

The shape of cells is altered to allow cells to adapt to their changing environments, including responding to internally generated and externally applied force. Force is sensed by cell surface adhesion proteins that are enriched in sites where cells bind to the extracellular matrix (focal adhesions) and neighboring cells (cell-cell or adherens junctions). Receptors at these adhesion sites stimulate intracellular signal transduction cascades that culminate in dramatic changes in the actin cytoskeleton. New actin filaments form, and/or new and existing filaments can be cleaved, branched, or bundled. Here, we discuss the actin cytoskeleton and its functions. We will examine the current understanding for how the actin cytoskeleton is tethered to adhesion sites. Finally, we will highlight recent studies describing how the actin cytoskeleton at these adhesion sites is remodeled in response to force.

Matrix Metalloproteinases Shape the Tumor Microenvironment in Cancer Progression

Cancer progression with uncontrolled tumor growth, local invasion, and metastasis depends largely on the proteolytic activity of numerous matrix metalloproteinases (MMPs), which affect tissue integrity, immune cell recruitment, and tissue turnover by degrading extracellular matrix (ECM) components and by releasing matrikines, cell surface-bound cytokines, growth factors, or their receptors. Among the MMPs, MMP-14 is the driving force behind extracellular matrix and tissue destruction during cancer invasion and metastasis. MMP-14 also influences both intercellular as well as cell-matrix communication by regulating the activity of many plasma membrane-anchored and extracellular proteins. Cancer cells and other cells of the tumor stroma, embedded in a common extracellular matrix, interact with their matrix by means of various adhesive structures, of which particularly invadopodia are capable to remodel the matrix through spatially and temporally finely tuned proteolysis. As a deeper understanding of the underlying functional mechanisms is beneficial for the development of new prognostic and predictive markers and for targeted therapies, this review examined the current knowledge of the interplay of the various MMPs in the cancer context on the protein, subcellular, and cellular level with a focus on MMP14.

Beta-Pix-dynamin 2 complex promotes colorectal cancer progression by facilitating membrane dynamics

PURPOSE

Spatiotemporal regulation of cell membrane dynamics is a major process that promotes cancer cell invasion by acting as a driving force for cell migration. Beta-Pix (βPix), a guanine nucleotide exchange factor for Rac1, has been reported to be involved in actin-mediated cellular processes, such as cell migration, by interacting with various proteins. As yet, however, the molecular mechanisms underlying βPix-mediated cancer cell invasion remain unclear.

METHODS

The clinical significance of βPix was analyzed in patients with colorectal cancer (CRC) using public clinical databases. Pull-down and immunoprecipitation assays were employed to identify novel binding partners for βPix. Additionally, various cell biological assays including immunocytochemistry and time-lapse video microscopy were performed to assess the effects of βPix on CRC progression. A βPix-SH3 antibody delivery system was used to determine the effects of the βPix-Dyn2 complex in CRC cells.

RESULTS

We found that the Src homology 3 (SH3) domain of βPix interacts with the proline-rich domain of Dynamin 2 (Dyn2), a large GTPase. The βPix-Dyn2 interaction promoted lamellipodia formation, along with plasma membrane localization of membrane-type 1 matrix metalloproteinase (MT1-MMP). Furthermore, we found that Src kinase-mediated phosphorylation of the tyrosine residue at position 442 of βPix enhanced βPix-Dyn2 complex formation. Disruption of the βPix-Dyn2 complex by βPix-SH3 antibodies targeting intracellular βPix inhibited CRC cell invasion.

CONCLUSIONS

Our data indicate that spatiotemporal regulation of the Src-βPix-Dyn2 axis is crucial for CRC cell invasion by promoting membrane dynamics and MT1-MMP recruitment into the leading edge. The development of inhibitors that disrupt the βPix-Dyn2 complex may be a useful therapeutic strategy for CRC.

Human Breast Extracellular Matrix Microstructures and Protein Hydrogel 3D Cultures of Mammary Epithelial Cells

Simple Summary

Human breast tissue extracellular matrix (ECM) is a microenvironment essential for the survival and biological activities of mammary epithelial cells. The ECM structural features of human breast tissues remain poorly defined. In this study, we identified the structural and mechanical properties of human normal breast and invasive ductal carcinoma tissue ECM using histological methods and atomic force microscopy. Additionally, a protein hydrogel was generated using human breast tissue ECM and defined for its microstructural features using immunofluorescence imaging and machine learning. Furthermore, we examined the three-dimensional growth of normal mammary epithelial cells or breast cancer cells cultured on the ECM protein hydrogel, where the cells exhibited biological phenotypes like those seen in native breast tissues. Our data provide novel insights into cancer cell biology, tissue microenvironment mimicry and engineering, and native tissue ECM-based biomedical and pharmaceutical applications.

Abstract

Tissue extracellular matrix (ECM) is a structurally and compositionally unique microenvironment within which native cells can perform their natural biological activities. Cells grown on artificial substrata differ biologically and phenotypically from those grown within their native tissue microenvironment. Studies examining human tissue ECM structures and the biology of human tissue cells in their corresponding tissue ECM are lacking. Such investigations will improve our understanding about human pathophysiological conditions for better clinical care. We report here human normal breast tissue and invasive ductal carcinoma tissue ECM structural features. For the first time, a hydrogel was successfully fabricated using whole protein extracts of human normal breast ECM. Using immunofluorescence staining of type I collagen (Col I) and machine learning of its fibrous patterns in the polymerized human breast ECM hydrogel, we have defined the microstructural characteristics of the hydrogel and compared the microstructures with those of other native ECM hydrogels. Importantly, the ECM hydrogel supported 3D growth and cell-ECM interaction of both normal and cancerous mammary epithelial cells. This work represents further advancement toward full reconstitution of the human breast tissue microenvironment, an accomplishment that will accelerate the use of human pathophysiological tissue-derived matrices for individualized biomedical research and therapeutic development.

Cell Trapping via Migratory Inhibition within Density-Tuned Electrospun Nanofibers

Cell migration is an essential bioprocess that occurs during wound healing and tissue regeneration. Abnormal cell migration is observed in various pathologies, including cancer metastasis. Glioblastoma multiforme (GBM) is an aggressive and highly infiltrative brain tumor. The white matter tracts are considered the preferred routes for GBM invasion and the subsequent spread throughout the brain tissue. In the present study, a platform based on electrospun nanofibers with a consistent alignment and controlled density was designed to inhibit cell migration. The observation of the cells cultured on the nanofibers with different fiber densities revealed an inverse correlation between the cell migration velocity and nanofiber density. This was attributed to the formation of focal adhesions (FAs). The FAs in the sparse fiber matrix were small, whereas those in the dense fiber matrix were large, aligned with the nanofibers, and distributed throughout the cells. A nanofiber-based platform with stepwise different fiber densities was designed based on the aforementioned observation. A time-lapse observation of the GBM cells cultured on the platform revealed a directional one-way migration that induced the entrapment of cells in the dense-fiber zone. The designed platform mimicked the structure of the white matter tracts and enabled the entrapment of migrating cells. The demonstrated approach is suitable for inhibiting metastasis and understanding the biology of invasion, thereby functioning as a promising therapeutic strategy for GBM.

Localization of KRAS downstream target ARL4C to invasive pseudopods accelerates pancreatic cancer cell invasion

Pancreatic cancer has a high mortality rate due to metastasis. Whereas KRAS is mutated in most pancreatic cancer patients, controlling KRAS or its downstream effectors has not been succeeded clinically. ARL4C is a small G protein whose expression is induced by the Wnt and EGF–RAS pathways. In the present study, we found that ARL4C is frequently overexpressed in pancreatic cancer patients and showed that its localization to invasive pseudopods is required for cancer cell invasion. IQGAP1 was identified as a novel interacting protein for ARL4C. ARL4C recruited IQGAP1 and its downstream effector, MMP14, to invasive pseudopods. Specific localization of ARL4C, IQGAP1, and MMP14 was the active site of invasion, which induced degradation of the extracellular matrix. Moreover, subcutaneously injected antisense oligonucleotide against ARL4C into tumor-bearing mice suppressed metastasis of pancreatic cancer. These results suggest that ARL4C–IQGAP1–MMP14 signaling is activated at invasive pseudopods of pancreatic cancer cells.

Most cases of pancreatic cancer are detected in the later stages when they are difficult to treat and, as a result, survival is low. Over 90% of pancreatic cancers contain genetic changes that increase the activity of a protein called KRAS. This hyperactive KRAS drives cancer growth and progression. Attempts to treat pancreatic cancer using drugs that reduce the activity of KRAS have so far failed.

The KRAS protein can accelerate growth in healthy cells as well as in cancer and it does this by activating various other proteins. Drugs that target some of these other proteins could be more effective at treating pancreatic cancer than the drugs that target KRAS. One of these potential targets is called ARL4C. ARL4C is active during fetal development, but it is often not present in adult tissues. Harada et al. investigated whether the protein is important in pancreatic cancer, and what other roles it has in the body, to better understand if it is a good target for cancer treatment.

First, Harada et al. used cells grown in the lab to show that ARL4C contributes to the aggressive spread of human pancreatic cancers. Using mice, Harada et al. also showed that blocking the activity of ARL4C in pancreatic cancers helped to slow their progression.

Harada et al.’s results suggest that ARL4C could be a good target for new drugs treating pancreatic cancers. Given that this protein does not seem to have important roles in the cells of adults, targeting it is unlikely to have major side effects. Further investigation of ARL4C in more human-like animal models will help to confirm these results.

Decoding leader cells in collective cancer invasion

Collective cancer invasion with leader-follower organization is increasingly recognized as a predominant mechanism in the metastatic cascade. Leader cells support cancer invasion by creating invasion tracks, sensing environmental cues and coordinating with follower cells biochemically and biomechanically. With the latest developments in experimental and computational models and analysis techniques, the range of specific traits and features of leader cells reported in the literature is rapidly expanding. Yet, despite their importance, there is no consensus on how leader cells arise or their essential characteristics. In this Perspective, we propose a framework for defining the essential aspects of leader cells and provide a unifying perspective on the varying cellular and molecular programmes that are adopted by each leader cell subtype to accomplish their functions. This Perspective can lead to more effective strategies to interdict a major contributor to metastatic capability.

Arsenic trioxide targets Hsp60, triggering degradation of p53 and survivin

The mechanisms of action of arsenic trioxide (ATO), a clinically used drug for the treatment of acute promyelocytic leukemia (APL), have been actively studied mainly through characterization of individual putative protein targets. There appear to be no studies at a system level. Herein, we integrate metalloproteomics through a newly developed organoarsenic probe, As-AC (C₂₀H₁₇AsN₄O₃S₂) with quantitative proteomics, allowing 37 arsenic binding and 250 arsenic regulated proteins to be identified in NB4, a human APL cell line. Bioinformatics analysis reveals that ATO disrupts multiple physiological processes, in particular, chaperone-related protein folding and cellular response to stress. Furthermore, we discover heat shock protein 60 (Hsp60) as a vital target of ATO. Through biophysical and cell-based assays, we demonstrate that ATO binds to Hsp60, leading to abolishment of Hsp60 refolding capability. Significantly, the binding of ATO to Hsp60 disrupts the formation of Hsp60-p53 and Hsp60-survivin complexes, resulting in degradation of p53 and survivin. This study provides significant insights into the mechanism of action of ATO at a systemic perspective, and serves as guidance for the rational design of metal-based anticancer drugs.

A highly selective organoarsenic fluorescent probe As-AC and quantitative proteomics were employed to track arsenic-binding and regulating proteins in live leukemia cells. Hsp60 was validated as a new target of ATO.

A metastasis suppressor Pt-dendrimer nanozyme for the alleviation of glioblastoma

Nanozymes are nanostructure-based materials which mimic the enzymatic characteristics of natural enzymes. Biological applications of nanozymes have been highlighted in basic research, industry, and translational medicine as a new cutting-edge tool. In this work, and for the first time, we disclose a tumor alleviation property of a nanozyme that is made up of amine-terminated sixth-generation polyamidoamine dendrimers with encapsulated tiny platinum nanoparticles. We systematically conducted the synthesis and characterization of the dendrimer-encapsulated Pt nanoparticles (denoted Pt-dendrimer) and confirmed their enzymatic function (hydrogen peroxide (H2O2) decomposition) within various cell lines (normal, cancerous), including glioblastoma (GBM) cells. By understanding the effects of the Pt-dendrimer at the gene level, especially related to cancer cell metastasis, we have thoroughly demonstrated its ability for tumor alleviation and suppressing GBM migration, invasion, and adhesion. The present findings show great promise for the application of the nanozyme for use in GBM-related basic research as well as at clinical sites.

From Microspikes to Stress Fibers: Actin Remodeling in Breast Acini Drives Myosin II-Mediated Basement Membrane Invasion

The cellular mechanisms of basement membrane (BM) invasion remain poorly understood. We investigated the invasion-promoting mechanisms of actin cytoskeleton reorganization in BM-covered MCF10A breast acini. High-resolution confocal microscopy has characterized actin cell protrusion formation and function in response to tumor-resembling ECM stiffness and soluble EGF stimulation. Traction force microscopy quantified the mechanical BM stresses that invasion-triggered acini exerted on the BM-ECM interface. We demonstrate that acini use non-proteolytic actin microspikes as functional precursors of elongated protrusions to initiate BM penetration and ECM probing. Further, these microspikes mechanically widened the collagen IV pores to anchor within the BM scaffold via force-transmitting focal adhesions. Pre-invasive basal cells located at the BM-ECM interface exhibited predominantly cortical actin networks and actin microspikes. In response to pro-invasive conditions, these microspikes accumulated and converted subsequently into highly contractile stress fibers. The phenotypical switch to stress fiber cells matched spatiotemporally with emerging high BM stresses that were driven by actomyosin II contractility. The activation of proteolytic invadopodia with MT1-MMP occurred at later BM invasion stages and only in cells already disseminating into the ECM. Our study demonstrates that BM pore-widening filopodia bridge mechanical ECM probing function and contractility-driven BM weakening. Finally, these EMT-related cytoskeletal adaptations are critical mechanisms inducing the invasive transition of benign breast acini.